I got the second one built up and working, but I can't manage to trim the ratio into spec. In 2:1, with the ratio trim pot maxed out and the threshold set to compress 2dB with -18dBfs input (-20dBfs output) I'm still seeing around -11 dBfs output when I feed it -8dBfs (I should be seeing -15dBfs). Same with 10:1 ratio - with the threshold set to compress 2dB with an input of -18dBfs (output of -20dBfs), I'm seeing around -15dBfs when I feed it -8dBfs (I should be seeing -19dBfs).
I double checked all the components and don't see any mistakes. I can only think of two possibilities:
1) the ratio trim pot, which only measures at around 415 ohms instead of 500 is too far out of spec and I need at least 500ohms.
2) the THAT 2181B's I bought aren't working as well as the ones I bought for the first one, years ago. Part of me is wondering if they're fake. I got them from Mouser, but the markings on them doesn't look like the ones I bought before, and look a bit smudged.
Anyone else have any ideas? Thanks!